As for a method of fabricating a film-like light polarizing device, there have so far been known three kinds of methods. A first method is a method of doping a poly(vinyl alcohol) (PVA) film that was drawn with a dichromic dye such as iodine, and so forth, as disclosed in Patent Document 1, i.e., JP-05-019247A (para No. 0008). This is a method whereby a PVA filmwith a dichromic substance, such as an iodine complex, adsorbed thereto is passed between rotating rollers to undergo uniaxial drawing while being heated, thereby aligning PVA molecules as well as the iodine complex. The film-like light polarizing device of such a makeup as described permits a light component having an oscillation plane orthogonal to a film-drawing direction to pass therethrough, absorbing a light component having an oscillation plane parallel with the film-drawing direction to be thereby lost, so that two sheets of the film-like light polarizing devices superimposed one on another appear black because the light components having all film fabricated by the first method is inexpensive, and is excellent in light quenching ratio, so that it is in widespread use in the current liquid crystal display device, and so forth, however, an application region thereof is limited to the visible light region.
A second method of fabricating a film-like light polarizing device is a method of dispersing two kinds of polymers or inorganic fine particles into a polymer to be subsequently subjected to uniaxial drawing as disclosed in Patent Document 2, i.e. JP-2002-022966A {claims, para Nos, (0033) to (0043)}. This is a method of, for example, causing respective refractive indexes of mixed substances to coincide with each other in a drawing direction while causing a refractive index difference Δn as large as possible to occur in the direction orthogonal to the drawing direction. In this case, in contrast with the method described, the refractive index difference Δn may be enlarged in the drawing direction while the refractive index difference Δn in the direction orthogonal to the drawing direction may be rendered as Δn=0. In either case, ideally the refractive index difference Δn in one direction is rendered as large as possible, that is, not less than 0.5, while the refractive index difference Δn in the other direction is rendered as Δn=0. However, it is extremely difficult to find out such a condition. Accordingly, with the second method of fabricating the light polarizing film, a light polarizing film small in area can be fabricated, but if there occurs a slight difference in localized reduction ratio by drawing, a refractive index difference Δn in a localized portion comes to differ from that in other portions, resulting in weakened polarizing function. Further, in order to obtain predetermined polarizing performance, there is the need for increasing the thickness thereof to some extent, which makes it difficult to obtain a high-performance light polarizing film small in thickness.
Then, a third method of fabricating a film-like light polarizing film is a method of obtaining light polarization property by arranging intervals of fine wires so as to be not longer than a wavelength of light to be polarized. A light polarizing film fabricated by this method is called a grid-type light polarizing film exhibiting an action as the light polarizing film if an interval d between the fine wires adjacent to each other is sufficiently shorter than a light wavelength λ, more specifically, if the fine wires are disposed at equal intervals of d<λ/2. The light polarizing film of this type has a function of reflecting a light component having an oscillation plane in the longitudinal direction of metal wires while transmitting a light component having an oscillation plane in the direction orthogonal to the longitudinal direction of the metal wires. Accordingly, this grid-type light polarizing film fabricated by the third method is contrary in operation principle to the film-like light polarizing device fabricated by the first method, and if two sheets of the grid-type light polarizing films are superimposed one on the other so as to cross each other at right angles, these act in effect like a mirror because incident light components having all the oscillation planes are reflected. With the grid-type light polarizing film, light transmittance thereof can be enhanced, however, electro-conductive fine wires and the intervals thereof need to be arranged so as to be not longer than the wavelength of light to be polarized. Hence, the grid-type light polarizing film has so far been used for infrared rays long in wavelength, and so forth, but has seldom been used for visible light because of difficulty with effecting polarization of the visible light.
By way of example of the grid-type light polarizing film described as above, in Patent Document 3, there is disclosed a method of fabricating a grid-type light polarizing film of a structure wherein metal is distributed in a grid pattern inside dielectrics, or on the surface thereof, fabricated by integrating two dielectrics with each other with the metal in the grid pattern interposed therebetween, and subsequently, by hot drawing or rolling the metal in whole, in the grid pattern, in a linear direction.
However, since the method of fabricating the grid-type light polarizing film, disclosed Patent Document 3, i.e., JP-9-090122 A {claims, para Nos, (0011) to (0021) FIG. 1}, requires heating up to a temperature causing the metal to expand, if a polymer substance is used for the dielectrics, the polymer substance will be in a melt condition or undergo depolymerization at such a temperature, so that it is impossible to fabricate the light polarizing film, and also, it is, in effect, difficult to enlarge the area thereof.
Still further, in Patent Document 4, i.e., JP-2001-074935 A {claims, para Nos, (0010) to (0014), FIG. 1, FIG. 2}, there is disclosed a grid-type light polarizing film of a structure comprised of metal portions and dielectric portions, anisotropic in shape, fabricated by forming a metal film on a transparent and soft substrate, and subjecting the substrate, and the metal film to drawing, at a temperature not higher than the melting point of the metal film.
With the method of fabricating the grid-type light polarizing film, disclosed Patent Document 4, however, as the transparent and soft substrate is uniformly drawn by drawing operation, an uniform drawing force also acts on the metal film on top of the substrate, so that metal wires formed out of the metal film will not be regularly arranged at intervals on the order of a light wavelength. More specifically, in the case of using a metal such as gold, excellent in ductility, the metal, together with the substrate, will be elongated to thereby keep covering the substrate, and on the other hand, in the case of using a metal such as aluminum, poor in ductility, irregular cracking will occur to the metal, or the metal will peel off the substrate, so tat there exists a problem that a polarization effect is hardly obtainable.
Furthermore, as disclosed Patent Document 5, i.e., JP-2003-529680A (claims), there has recently been made public a method of fabricating a light polarizing film for a visible light region by forming fine grooves on a glass sheet with the use of a photo resist, and by vapor-depositing a metal thereon, however, with this method, fabrication cost becomes high because of a complex fabrication process involved, and moreover, it is practically impossible to increase an area to 5 cm2 or larger.
Thus, with the method of fabricating the grid-type light polarizing film, described as above, only the grid-type light polarizing film with an area several cm2 at the maximum has been obtained, and it has been impossible to obtain a film-like light polarizing device of the grid-type with an area larger than the area described as above. Hence, there has been a strong demand for a film-like light polarizing device of the grid-type, large in area, with the polarization effect thereof enhanced in a range from a visible light region to an infrared region, having a structure wherein there are alternately disposed electro-conductors, and dielectrics, each having a width on the order of 1/10 of a wavelength in use, that is, in a range of several 10 nm to several μm, and a length not less than 10 times as long as the wavelength in use, that is in a range of several hundred nm to several hundred μm.